1. Field of the Invention
The present invention relates to a transmitter adjusting output power, and more particularly to a transmitter which, driven by a battery as in the handset of a mobile telephone, adjusts output power so as to minimize the exhaustion of the power source battery when adjusting the output power of transmit signals.
2. Description of the Related Art
Usually, a cordless mobile telephone, when communicating with another mobile telephone, is subject to fluctuations in the field intensity of the receive wave reaching each mobile telephone depending on the distance between the calling party's mobile telephone and the corresponding telephone relaying base and the state of the wave transmission in-between, as well as the distance between the other party's mobile telephone and the corresponding telephone relaying base and the state of the wave transmission in-between.
If the field intensity of the receive wave reaching the calling party's mobile telephone is weak, the link with the other party may be so affected by noise and the like that satisfactory communication is difficult or sometimes even impossible. On the other hand, if the field intensity of the receive wave reaching the calling party's mobile telephone is strong, the transmission/reception of the wave may be taking place at a signal level which is higher than the necessary signal level. This is not desirable because the exhaustion of the power source battery of the mobile telephone would correspondingly increase.
For this reason, in order to ensure satisfactory communication between one mobile telephone and the other mobile telephone, and to avoid an unnecessary increase in battery exhaustion, when a wave transmitted from the other mobile telephone is received, the field strength of the receive wave should be detected. If the detected field strength is relatively large, the signal gain of the transmitter should be adjusted according to the relative level of the detected field strength to reduce the level of the transmit signal from the transmitter. If the detected field strength is relatively weak, the signal gain of the transmitter should be adjusted according to the relative level of the detected field strength to enhance the level of the transmit signal from the transmitter. Thus, by adjusting the level of the transmit signal sent from the respective transmitters of two mutually communicating mobile telephones, the field strength of the wave received by each other's mobile telephone can be regulated to a standard level, thereby enabling the two mobile telephones to communicate satisfactorily and prevent both mobile telephones from suffering unnecessary exhaustion of their respective power source batteries.
Know adjusting means for signal gains of transmitters in mobile telephone include a first gain adjusting means which fixes the signal gain in the power amplifying stage and makes controllable the signal gain in the drive amplifying stage with a gain control voltage to adjust the level of the transmit signal as required; and also known is a second gain adjusting means which fixes the signal gain in the drive amplifying stage and makes controllable the signal gain in the power amplifying stage with a gain control voltage to adjust the level of the transmit signal as required.
FIG. 3 is a block diagram illustrating the configuration of essential parts of a transmitter using a first gain adjusting means in a known mobile telephone.
As shown in FIG. 3, this transmitter is provided with a fixed-gain power amplifying stage (PA) 31, a variable-gain drive amplifying stage (DA) 32, a transmit signal generator 33, a gain control voltage generator 34, a transmit signal output terminal 35 and a transmit data (TX data) input terminal 36. Of the transmit signal generator 33, the input terminal is connected to the transmit data input terminal 36 and the output terminal is connected to the input terminal of the variable-gain drive amplifying stage 32. Of the variable-gain power amplifying stage 32, the control terminal is connected to the output terminal of the gain control voltage generator 34 and the output terminal is connected to the input terminal of the fixed-gain power amplifying stage 31. Of the fixed-gain power amplifying stage 31, the output terminal is connected to the transmit signal output terminal 35.
In this case, the transmit signal generator 33 forms a carrier frequency, and modulates the formed carrier frequency with transmit data (TX data) supplied to the transmit data input terminal 36 to generate a transmit signal, and the generated transmit signal is supplied to the variable-gain drive amplifying stage 32 that follows. The gain control voltage generator 34 generates a gain control voltage corresponding to the level of the receive signal that has been received (the field strength of the receive wave), and the gain control voltage so obtained is supplied to the variable-gain drive amplifying stage 32. Further, the transmit signal output terminal 35 is connected to a transmission antenna (not shown in FIG. 3).
Schematically, the transmitter using the first gain adjusting means having the above-described configuration operates in the following manner.
As the receiver (not shown in FIG. 3) of a mobile telephone receives a signal transmitted by the mobile telephone of the other party to the call, the controller (not shown in FIG. 3 either) detects a receive signal level representing the field strength of the receive wave. If the detected receive signal level is relatively low, the gain control voltage generator 34 generates a gain control signal to increase the signal gain of the variable-gain drive amplifying stage 32 according to the relative level of the receive signal level, and supplies it to the variable-gain drive amplifying stage 32. If the detected receive signal level is relatively high, the gain control voltage generator 34 generates a gain control signal to reduce the signal gain of the variable-gain drive amplifying stage 32 according to the relative level of the receive signal level, and supplies it to the variable-gain drive amplifying stage 32. After that, the variable-gain drive amplifying stage 32 amplifies the transmit signal supplied from the transmit signal generator 33 with a signal gain corresponding to the gain control signal, and supplies the amplified signal to the power amplifying stage 31. The power amplifying stage 31 further amplifies in power the supplied transmit signal, and supplies the amplified transmit signal to the transmission antenna via the transmit signal output terminal 35 to cause it to be transmitted from the transmission antenna. The transmit signal level required then is so controlled as to be raised when the receive signal level is too low and, conversely, to be lowered when the receive signal level is too high.
Hereupon, FIG. 4 shows the relationship between the transmit signal level (output power) of a transmitter using the first gain adjusting means and the current consumption by the power amplifying stage 31.
As illustrated in FIG. 4, in the transmitter using the first gain adjusting means, when the required transmit signal level is in a high range, the current consumption by the power amplifying stage 31 increases. In this case, if the required transmit signal level is within the range from 3 to 10 dBm, the rate of variation of the current consumption dependent on the variation of the required transmit signal level is relatively mild, remaining between 30 and 40 mA, but if the required transmit signal level exceeds 10 dBm to approach or reach 24 dBm, the rate of variation of the current consumption dependent on the variation of the required transmit signal level increases to an approximate range of 40 mA to 160 mA.
Next, FIG. 5 is a block diagram of essential parts of a transmitter using a second gain adjusting means in a known mobile telephone.
As illustrated in FIG. 5, this transmitter is provided with a variable-gain power amplifying stage (PA) 41, a fixed-gain drive amplifying stage (DA) 42, a transmit signal generator 43, a gain control voltage generator 44, a transmit signal output terminal 45 and a transmit data (TX data) input terminal 46.
Of the transmit signal generator 43, the input terminal is connected to the transmit data input terminal 46 and the output terminal is connected to the input terminal of the variable-gain power amplifying stage 42. The output terminal of the fixed-gain drive amplifying stage 42 is connected to the input terminal of the variable gain power amplifying stage 41. In the variable gain power amplifying stage 41 the output terminal is connected to the transmit signal output terminal 45 and the control terminal is connected to the output terminal of the gain control voltage generator 44.
Also in this case, the transmit signal generator 43 forms a carrier frequency, and modulates the formed carrier frequency with transmit data (TX data) supplied to the transmit data input terminal 46 to generate a transmit signal, and the generated transmit signal is supplied to the drive amplifying stage 42 that follows. The gain control voltage generator 44 generates a gain control voltage corresponding to the level of the receive signal that has been received (the field strength of the receive wave), and the gain control voltage so obtained is supplied to the variable-gain power amplifying stage 41. Further, the transmit signal output terminal 45 is connected to a transmission antenna (not shown in FIG. 5).
Schematically, the transmitter using the second gain adjusting means having the above-described configuration operates in the following manner.
As the receiver (not shown in FIG. 5) of a mobile telephone receives a signal transmitted by the mobile telephone of the other party to the call, the controller (not shown in FIG. 5 either) detects a receive signal level representing the field strength of the receive wave. If the detected receive signal level is relatively low, the gain control voltage generator 44 generates a gain control signal to increase the signal gain of the variable-gain power amplifying stage 41 according to the relative level of the receive signal level, and supplies it to the variable-gain power amplifying stage 41. If the detected receive signal level is relatively high, the gain control voltage generator 44 generates a gain control signal to reduce the signal gain of the variable-gain power amplifying stage 41 according to the relative level of the receive signal level, and supplies it to the variable-gain power amplifying stage 41. After that, the variable-gain drive amplifying stage 42 amplifies the transmit signal supplied from the transmit signal generator 43, and supplies the amplified signal to the variable-gain power amplifying stage 41. The variable-gain power amplifying stage 41 amplifies in power the supplied transmit signal with a signal gain corresponding to the gain control signal, and supplies the amplified transmit signal to the transmission antenna via the transmit signal output terminal 45 to cause it to be transmitted from the transmission antenna. The transmit signal level required then is so controlled as to be raised when the receive signal level is too low and, conversely, to be lowered when the receive signal level is too high.
Here, FIG. 6 shows the relationship between the transmit signal level (output power) of a transmitter using the second gain adjusting means and the current consumption by the power amplifying stage 41.
As illustrated in FIG. 6, in the transmitter using the second gain adjusting means, like the transmitter using the first gain adjusting means, when the required transmit signal level is in a high range, the current consumption by the power amplifying stage 41 increases. In this case, if the required transmit signal level is within the range from 2 to 12 dBm, the rate of variation of the current consumption dependent on the variation of the required transmit signal level is relatively mild, remaining between 10 and 35 mA. However if the required transmit signal level exceeds 12 dBm to approach or reach 24 dBm, the rate of variation of the current consumption dependent on the variation of the required transmit signal level increases to an approximate range of 35 mA to 160 mA.
By comparing the characteristic diagram of FIG. 4 with that of FIG. 6, if the required transmit signal level is within the range from 2 to 19 dBm, the transmitter using the second gain adjusting means consumes somewhat less current in its power amplifying stage, while in the transmit signal level range from 19 to 24 dBm, the transmitter using the first gain adjusting means consumes slightly less current in its power amplifying stage.
Since a cordless mobile telephone uses a battery as its power source, when the mobile telephone is used beyond a certain length of time, its battery becomes exhausted and the mobile telephone can no longer be used. For this reason, it is required that the power source battery of a mobile telephone be extended in durability as long as practicable to ensure a long service life of the telephone, and this requirement applies similarly to a mobile telephone having a transmitter using the first gain adjusting means and one having a transmitter using the second gain adjusting means, both described above.
In a mobile telephone having a transmitter using the first gain adjusting means or one having a transmitter using second gain adjusting means, their respective variable gain amplifying stages 32 and 41 are so adjusted as to achieve the required transmit signal level according to the relative level of the receive signal, the service life of the power source battery is extended by reducing the current consumption of the variable gain amplifying stage 32 or 41 when the required transmit signal level is adjusted to be relatively low, but the elongation of the battery's life is not sufficient and, by no means satisfactory.